1. Field of the Invention
This invention relates to a method and apparatus for quick and aseptic filtration of a nutrient solution during the supply of nutrient of a microorganism to a fermentor or a culture broth and during the collection of the supernatant of the broth from the fermentor. The term "supernatant" as used in this invention means the supernatant of culture broth.
2. Description of the Prior Art
As filter media heretofore used in supernatant collecting devices attached to or inserted into fermentors, or in medium feeding devices installed for supply of aqueous nutrient solution of microorganisms to fermentors, there are known (1) a filter medium formed of polyvinyl alcohol series hollow fibers, (2) a filter medium made of sintered metal, and (3) a filter medium formed of nitrocellulose series polymer membrane. The known media have defects when used. The polyvinyl alcohol series hollow fibers offer poor resistance to heat and undergo degradation at elevated temperatures and, therefore, do not withstand sterilization at temperatures exceeding 100.degree. C. such as in an autoclave. The filter medium using the sintered metal is resistant to heat. When it is left standing in a culture broth for long time, however, the metal of the filter medium is dissolved by ionization and consequently causes detrimental transformation of the components of the culture medium and adversely affects the microorganism in the broth. Also the sintered metal itself undergoes degradation due to the ionization and fails to offer long service life. The nitrocellulose series polymer membrane, though excellent in heat resistance and durability, is deficient in membrane strength and porosity and, from the standpoint of membrane strength, is incapable of sampling a supernatant by vacuum suction with the aid of a syringe or pump.